1. Field of the Invention
The invention concerns a device for adjusting the checking unit of a presser foot of a sewing and/or embroidery machine.
2. Background Art
Throughout the following specification and claims, the terms xe2x80x9ccheckingxe2x80x9d and xe2x80x9ccheckxe2x80x9d and xe2x80x9ccatchingxe2x80x9d and xe2x80x9ccatchxe2x80x9d may be used interchangeably.
An embroidery machine of this type with a checking unit for a presser foot is known from DE 3117140. The checking unit disclosed in DE 3117140 achieves a situation in which the presser foot no longer strikes the workpiece to be machined and therefore the needle plate with the full force derived from the needle bar drive and transferred via the spring inserted in between, but is checked shortly before contact, a large part of the force residing in the movement of the presser foot being absorbed before the presser foot is released to perform the remaining movement with a certain time delay. The checking unit achieves a significant attenuation of the noise and protects the workpiece and/or the embroidery from damage caused by long term stress from the presser foot. The checking unit consists substantially of a control cam, which activates an angled lever, the one arm of which checks the presser foot, accelerated by a spring in the direction of the workpiece, via a checking component and releases the said foot with a time delay so that the presser foot is braked when it strikes the workpiece.
It is disadvantageous in the case of the checking unit known from DE 3117140 that, resulting from the rigid structure, the movement path of the presser foot is identical for different thicknesses of workpiece so that in the presence of relatively large workpiece thicknesses, the presser foot strikes the surface of the workpiece with too much force so that the advantages of the checking unit are reduced.
A device is described in DE 19628524, with which the presser foot is moved into a safe position after the sewing process. No adjustment to material thicknesses is provided.
A very time-consuming and expensive way is described in DE 4302094 in which the presser foot is moved via a separate drive motor thus permitting any desired movement paths and therefore adjustment to different thicknesses of material to be implemented. However, the additional drive requires a time-consuming synchronisation of the two drives for the needle bar and the presser foot.
DE 4324741 and DE 2938894 show checking units for presser foot attachments in which the movement path of the presser foot can be adjusted to the thickness of the material. It is disadvantageous in these units that they utilise complicated lever systems which have an expensive structure and are prone to breakdowns. Increased demands are imposed on the tolerances to be met because of the large number of moving parts and a relatively large amount of noise is created.
The object of the present invention is therefore to provide a checking unit for a presser foot of a sewing machine which is of a simple structure and permits an adjustment to a very wide range of workpiece thicknesses.
This object is achieved according to the invention by a device with the characteristics of claim 1.
It is advantageous in the device according to the invention that the position of the bearing of the checking element, which works in direct combination with the presser foot, is changed manually or automatically and held and/or locked in a specific position. As a result, no additional elements are necessary which have to be arranged in the force transmission region between the checking element and the drive for the checking element. The adjustment of the position of the bearing of the checking element, which is preferably an angled lever, should be able to be moved to at least two positions or any desired location between two positions and/or should be able to be locked.
In a particular embodiment of the device, the bearing and/or the swivelling axle of the checking element can be swivelled around an axis, so that the position of the checking element alters relative to the needle plate depending on the angle set. To do this, the bearing of the checking element itself is mounted in a cylinder coaxial to the latter""s axis, whereby the cylinder is mounted so that it can rotate around its axis on the sewing or embroidery machine.
If the cylinder is turned, the bearing which, for example may be a bolt, which is mounted so that it rotates in the cylinder coaxial to its axis, is moved around the axis, whereby the position of the bearing and/or the bearing bolt changes in respect of the needle plate. This permits an advantageous thickness adjustment of the presser foot to the workpiece or embroidery by simple means. The cylinder itself is can be locked in any desired angle positions or at specific engaging points by means of fixing screws or locking teeth which for example can be raised against a spring force.
The angle adjustment of the cylinder, mounted so that it can rotate, which holds the bearing for the checking element, can be performed automatically by means of a drive in a further advantageous embodiment of the invention.
In a further embodiment, the bearing for the checking element is not mounted so that it can swivel around an axis but is able to be locked in various positions especially parallel to the needle bar e.g. in a longitudinal slot. Moving the bearing in the longitudinal slot may be undertaken manually or automatically by means of a drive as in the embodiments described above.
In a further form of the embodiments described above, the material thickness close to the presser foot is determined underneath the presser foot by means of a sensor and the position of the checking element is regulated to correspond automatically by means of a drive. This has the advantage of guaranteeing that even in the case of a workpiece which has different degrees of thickness at different points, the presser foot always strikes the workpiece in the bast possible way during the embroidery or sewing process.